The National Security Agency's wide-reaching Internet surveillance dragnet sweeps up more ordinary Internet users' communications than previously thought, according to a new report.

Nine out of 10 people on which the NSA spied were not actually the intended targets of its surveillance, and nearly half of the surveillance files either belonged to U.S. citizens or residents, a Washington Post investigation revealed.

Published on Saturday, the report is based on a treasure trove of 160,000 intercepted conversations, including more than 120,000 instant messages, roughly 22,000 emails and nearly 4,000 social-network messages coming from 11,400 unique accounts. The conversations spanned from 2009 to 2012, and were provided to The Post by former NSA contractor Edward Snowden. They were collected using Internet-surveillance programs such as PRISM and the Upstream collection, a set of surveillance programs that tap directly into the Internet backbone.

The investigation highlights how the NSA's spying activities — even when focused on legitimate security targets — ended up ensnaring the conversations of many innocent Internet users. Although the surveillance files analyzed by The Post did result in the capture of some terrorist suspects, in many cases, they "have a startlingly intimate, even voyeuristic quality," the newspaper said.

Among the files, there are medical records, lovers' chat messages, photos of toddlers, and images of scantily clad men and women. Some of these people got swept up in the NSA's surveillance dragnet because they interacted directly with a target, or because they were part of the same chat room as a target.

To spy on the content of Americans' communications, the NSA normally has to get an individual warrant, but for foreigners, no warrant is needed. Many of these communications got swept up because the NSA had lax criteria when it came to judging whether a target was an American or a foreigner, according to The Post.

NSA analysts assumed that emails written in a different language belonged to foreigners, or that all people on a foreign's contact list were also foreigners, The Post said.

The investigation puts last week's NSA transparency report in perspective. In the report, the Office of the Director of National Intelligence, the agency overseeing all American spy agencies, said the NSA spied on nearly 90,000 targets in 2013.

However, according to Snowden's new documents, dated from 2009 to 2012, the proportion of targets to non-targets was 1 to 9. If this ratio was the same in 2013, it would mean the NSA collected Internet communications of around 810,000 people last year.

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